FIGS. 1a through 1d are schematic flow diagrams showing the process for manufacturing a conventional vertical light-emitting diode. A sapphire substrate 100 is first provided. Next, an illuminant epitaxial structure 102 is formed on a surface of the sapphire substrate 100 by an epitaxial method, such as shown in FIG. 1a. Typically, the illuminant epitaxial structure 102 is mainly composed of a first conductivity type semiconductor layer, an active layer and a second conductivity type semiconductor layer. Because the sapphire substrate 100 is made of an electrically insulating material, another conductive substrate 104 usually has to be provided and the electrically insulating sapphire substrate 100 is removed when a vertical connecting electrode structure is fabricated. After the illuminant epitaxial structure 102 is completed, the illuminant epitaxial structure 102 is adhered to the conductive substrate 104 by a bonding method, such as shown in FIG. 1b. 
After the illuminant epitaxial structure 102 is bonded to the substrate 104, the whole sapphire substrate 100 is removed from the illuminant epitaxial structure 102 by a laser ablation technique, so as to expose a surface of the illuminant epitaxial structure 102, such as shown in FIG. 1c. Then, a first conductivity type electrode 106 and a second conductivity type electrode 108 are respectively formed on the illuminant epitaxial structure 102 and the substrate 104. Subsequently, a dicing step is performed to form a plurality of light-emitting diode chips 110, such as shown in FIG. 1d. 
However, in the aforementioned process of the light-emitting diode, when the laser ablation technique is used to remove the sapphire substrate 100, a stress, which is caused by the high temperature or large temperature difference during the laser treating process, damages the structure of the light-emitting diode. Moreover, the device quality is degraded by the excessively large energy transfer induced in the ablation process. Therefore, the operation quality and the product yield of the light-emitting diode are decreased. In addition, the ablation rate of the substrate is very slow, so it takes a long time to ablate the whole substrate, which increases the process cost and reduces the throughput. Besides, this process requires bonding the illuminant epitaxial structure to the additional substrate 104, further increasing cost and lowering yield.